The present invention relates generally to the regulation of the temperature of a fluid that is to be delivered to a specific target location within a body structure. More particularly, the invention provides methods and apparatus for altering the temperature of a fluid that is to be delivered to the target location while the fluid is within the patient.
On many occasions, the temperature of a fluid within a patient needs to be regulated. For example, in some medical procedures, various fluids, such as solutes or drugs, are delivered to target locations within the body. The desired temperature of these fluids upon delivery may vastly differ from the storage temperature. In such cases, it is therefore desirable to heat or cool the fluid before it reaches the target location. Although possible to heat or cool the fluid outside of the patient, such a procedure can be cumbersome and require elaborate equipment.
As another example, fluids at various temperatures may be introduced to a target location within a patient to regulate the temperature of a localized area within a body structure. One particular application where the heating or cooling of a specific area within a body structure is desirable is in the field of neurosurgery. In many cases, it is desirable to cool a specific area within the brain prior to performing a surgical procedure.
As a further example, the temperature of body fluids may be regulated to control the patient's body temperature. The regulation of the patient's body temperature is particularly useful in treating patient's suffering from either hypothermia or hyperthermia.
Under ordinary circumstances, the thermal regulatory system of the human body maintains a near constant temperature of about 37.degree. C. (98.6.degree. F.). Heat lost to the environment is precisely balanced by heat produced within the body. Hypothermia is a condition of abnormally low body temperature. Hypothermia can be clinically defined as a core body temperature of 35.degree. C. or less. Accidental hypothermia results when heat loss to the environment exceeds the body's ability to produce heat internally. Hypothermia may also occur in patients exposed to mild cold stress whose thermal regulatory ability has been lessened due to injury and illness.
Hypothermia of either type is a dangerous condition which can have serious medical consequences. In particular, hypothermia interferes with the ability of the heart to pump blood. Hypothermia may be fatal for this reason alone. Additionally, low body temperatures seriously interfere with the enzymatic reactions necessary for blood clotting. This sometimes results in bleeding that is difficult to control, even when normal clotting factor levels are present. These effects and other adverse consequences of hypothermia lead to drastically increased mortality rates both among victims of trauma and in patients undergoing surgery.
Hyperthermia is a condition of abnormally high body temperature and may result from exposure to a hot environment, overexertion, or fever. Body core temperatures can range from 38.degree. C. to 41.degree. C. due to fever and may be substantially higher in cases of exposure and overexertion. Like hypothermia, hyperthermia is a serious condition and can be fatal.
Simple methods for treating both hypothermia and hyperthermia have been known since early times. In the case of hypothermia, such methods include wrapping the patient in blankets, administering warm fluids by mouth, and immersing the patient in a warm water bath. To treat hyperthermia, some have proposed immersion of the patient in a cool water bath or the administration of cool fluids. However, such methods can have serious drawbacks and limited effectiveness.
One particular catheter structure which has been developed to treat a patient suffering from either hypothermia or hyperthermia is described in U.S. Pat. No. 5,486,208, the complete disclosure of which is herein incorporated by reference. Such a catheter has the ability to heat or cool a liquid that is circulated through a catheter body.
Although such a catheter has been shown to be generally effective in the treatment of both hypothermia and hyperthermia, some improvements are still desired. For example, it would be desirable if such a catheter were more versatile to allow for the temperature of various fluids introduced into the body to be regulated. In this manner, the temperature of an introduced fluid could be more closely controlled at the point of introduction. It would be further desirable if a catheter structure and methods were provided for regulating the temperature of a localized region within a body structure prior to performing a medical procedure on the body structure.